FMCW radar systems are presently used in a plurality of applications. For example, FMCW radar systems, in particular, may be used in motor vehicles. FMCW radar systems in motor vehicles are, for example, used to detect objects which are located in the surroundings of the motor vehicle. The data received by the FMCW radar systems regarding objects which are located around the vehicle may then be used, for example, for automatic cruise control of a motor vehicle.
FMCW radar systems make it possible to determine a speed and a distance of an object relative to the FMCW radar system. For this purpose, multiple modulations are transmitted by the radar and the reflected radar signals are evaluated. A series of transmitted modulations (radar signals) is referred to as a sequence. Here, the individual modulations are each characterized by different modulation parameters, in particular by a modulation slope of the transmission frequency. For example, a modulation may have a modulation slope of 400 MHz/ms.
For object recognition, usually a plurality of modulations of radar signals is transmitted. The modulations may have identical or different modulation parameters.
Since radar systems are in general based on transmitting electromagnetic waves and detecting and evaluating the reflections of these transmitted electromagnetic waves from objects, radar systems are susceptible to interferences of other radar systems. Interferences are mutual disruptions of radar systems. Interferences may, for example, delimit the sensitivity of a radar sensor or have an influence on its detection range. Furthermore, an interference may result in an erroneous recognition or non-recognition of objects.
In modern radar systems, methods for detecting interferences are thus used.
U.S. Published Patent Application No. US 2007/0018886 A1 describes an interference recognition method in which interferences are detected based on a rate of change of the amplitude of the received radar signal.
Furthermore, Japanese Patent Application No. JP 2002 168947 (A) describes a method for interference recognition in which a threshold value is established for the output signal of a mixer of a receiver unit. If the level of the output signal exceeds the threshold value, an interference is assumed. The threshold value is determined as a function of a relative speed or a distance between the radar system and a detected object.